Off Brand Thermostat: A Cautionary Tale with Lingering Questions.
 

Had a crack in my stock thermostat housing. Tried to find a mopar replacement locally and no one had them. The dealer told me they were back ordered by 6 months. Anyone online who had it in-stock were a week in shipping. So…

Mistake #1: I bought an off brand thermostat and installed it.

After a few days I noticed it was running a little hot. My assumption was that the off brand part wasn’t opening all the way. I tracked down the proper mopar part and got it on order. But in the meantime I carefully monitored the engine temp over several days and it wouldn’t jump higher than 245 under hard acceleration.

Mistake #2: I assumed the malfunction was stable. It was not.

It worked fine for for the next 3 days, until it catastrophically failed about 3 miles from home, redlining the temp gauge. I was close to a gas station so I pulled in to let it cool, and bought a couple gallons of water. Only put about a third of gallon in before it was full up. IR temp test on the radiator was 70degrees. There was pressure in the upper radiator hose, and the hose read 210 on the exterior with the IR gun, but it seemed clear that the thermostat was barely opening at all anymore. I was only three miles from home, so I waited a bit for it to cool off before attempting to hobble my way home. After another mile, it redlined again. Except, this time the temp gauge went dead, and the electronic throttle control light popped on. I again pulled over to let it cool, and added as much water as it would let me, about a gallon. I was on an incline and attempted to burp the system as best I could by turning the car on for just a few seconds at a time to get air out. After waiting 15 min, I tried turning the car back on, but still had no temp gauge.

Mistake #3: I didn’t have the patience to wait for total cooldown.

I made the assumption that the overheating had damaged the temp sensor, and that the engine had probably cooled down enough. I decided to just take it easy but proceed home. Which was fine until I pulled in the drive and the engine started sounding funky. A little bit of uneven hesitation and a ticking that normally isn’t there could be heard. Trying to engage the clutch to pull the rest of the way in the drive off the main road made a bad chattering sound, similar to the sound an engine with bad motor mounts hitting on the fan. I immediately turned the engine off. And in my panic I did the dumbest thing yet.

Mistake #4: I grabbed the garden hose and sprayed down the engine in a total panic move to bring down the temp.

In retrospect, this was a really dumb thing to do. I’m an engineer, I should know better than that. I know full well how damaging a rapid cool can be. I just wasn’t thinking straight. After that I let it cool off completely, probably an hour plus. I then pulled the thermostat out and boil tested it. It failed miserably. It didn’t open at all. I pulled out the internals and reinstalled the housing without the valve. I put it all back together, topped off the radiator, said a prayer, and tried starting the engine.

The Good News: It started up just fine. It a purred like a kitten. No weird noises or vibrations at all. The temp gauge was back working, and the throttle control light was off.

I went ahead burping the coolant system to remove air. And proceeded to test at idle for an hour. It got up to 212 before the fan started to cycle correctly, producing a steady temp cycle. All seems to be functioning as it should.

The Lingering Questions:

What tests should I be doing, and what problems should I be looking for? I don’t want to cause any further issues by ignoring possible damage that may have occurred.

I’m planning a through coolant flush (my heater core needed it anyway), and I’m thinking an oil change might not be a bad idea. Anything else I should consider swapping? Manual transmission, is there any reason to swap that fluid? Transfer case?

Any incite would be appreciated. Thanks.

Thermostat
 

I installed a Dorman 902-852 thermostat on my 2013 due to a coolant temp OBD code. It's only been 2 weeks but no issues so far and the code has no returned. FYI.

just a suggestion... if the engine got that hot, might want to change the oil and filter also.....

^ that oil will be toast/sludge fest, and the filter will likely be failing internally.
If it were me, I would toss a second oil change after a couple hundred miles with another fresh filter.

The manual transmission doesn't have anything to do with the cooling system on my 2007, and the same with the transfer case. I think they will be fine, but I don't know a thing about 2015 JKs. If you want to change those fluids go ahead, it isn't a tough job. Just did both mine recently. Buy a little quart bottle pump to put on your quarts of oil if you do. Recommend Amsoil synchromesh for the manual transmission. My biggest concern about overheating is warped heads. If you have the stuff to pressure test your coolant system I would do that. When you do change the oil and filter make sure it doesn't look like any water in the oil. Thanks for the advice, on aftermarket thermostats.

Yeah, I was thinking an oil change would be smart. I’ll definitely do that. Though to be honest, I checked it and it didn’t look that burnt on the dipstick. So maybe that’s a good sign?

@Seizer What pressure am I looking to see for the coolant pressure test? I tried searching for a write up and couldn’t find anything. I can probably rent equipment from an o’rileys or AutoZone.

What’s the best way to check for a warped head? Leak down test? Never done one, but I’m sure I could look it up.

Zxkn, certainly a leak down test or coolant pressure check would check for warped heads, before all that, a close look at the coolant in the radiator (checking for any sign of oil) or the reverse check the oil (when doing the change) for any minute signs of coolant in the oil (usually shows as foam) . I think a simple compression check would provide more information quicker than a leak down test or coolant pressure check. Just pulling spark plugs will tell a story... if they come out and show dark brown or black your good, if they come out looking white or tan you got water in the cylinder.

Coolant pressure test should not be much more than 20psi.

What Sixty4X4 said, and my radiator cap says 18LBs, so check your radiator cap.
Can watch this video for a quick run down.

I actually like XJRefugee's suggestion better than mine.

So:

I changed the oil, no sign of water in it. Seem to be good there.

I haven’t done compression test yet, because I haven’t wanted to pull the intake to get to the driver side plugs.

I did do a coolant pressure test. Not sure how to interpret the results. Cap says 18psi, pumped up to that pressure. After 15min, it slowly dropped to 17psi. At 30min it had dropped to 16psi. After an hour and a half, it had dropped to 15psi.

Does that sound normal or do I have a small leak? I know you can get a kit to test for exhaust gases in the coolant. Would it be worth doing that?